V. Hazardous as deathbed repentance is, the grace of absolution must not be refused even when it can be asked for only by signs.
Hence it behooves each individual Christian to listen to the judgment of his own conscience, lest he put off the turning to God from day to day and fix the time of his amendment at the end of his life; for it is most perilous for human frailty and ignorance to confine itself to such conditions as to be reduced to the uncertainty of a few hours, and instead of winning indulgence by fuller amendment, to choose the narrow limits of that time when space is scarcely found even for the penitent's confession or the priest's absolution.
But, as I have said, even such men's needs must be so assisted that the free action of penitence and the grace of communion be not denied them, if they demand it even when their voice is gone, by the signs of a still clear intellect. And if they be so overcome by the stress of their malady that they cannot signify in the priest's presence what just before they were asking for, the testimony of believers standing by must prevail for them, that they may obtain the benefit of penitence and reconciliation simultaneously, so long as the regulations of the Father.' canons be observed in reference to those persons who have sinned against God by forsaking the Faith.
Source: Letters (New Advent)